Wireless communication systems have become an important means by which many people worldwide have come to communicate. A wireless communication system interconnects many nodes by using electromagnetic waves, such as radio waves, rather than wires commonly used in a fixed telephone network system. A wireless communication system often consists of many mobile devices and a plurality of base stations. A base station serves a mobile device when it enters a region associated with the base station.
Wireless communication systems are widely used to provide voice and data services for multiple users using a variety of access terminals such as cellular telephones, laptop computers and various multimedia devices. Such communications systems can encompass local area networks, such as IEEE 801.11 networks, cellular telephone and/or mobile broadband networks. The communication system can use one or more multiple access techniques, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA) and others. Mobile broadband networks can conform to a number of standards such as the main 2nd-Generation (2G) technology Global System for Mobile Communications (GSM), the main 3rd-Generation (3G) technology Universal Mobile Telecommunications System (UMTS) and the main 4th-Generation (4G) technology Long Term Evolution (LTE).
As technologies evolve, multiple input, multiple output (MIMO) systems are employed to achieve better channel utilization and overall performance. In particular, MIMO systems are communication systems having multiple transmission and multiple reception antennas at both enhanced Node B (eNB) (or base station (BS), Node B (NB, and so forth) and user equipment (UE) (or mobile station (MS), terminal, terminal device, user, subscriber, subscriber equipment and so on). In a MIMO system, a transmitter may transmit a multiple user MIMO signals to a plurality of receivers. Each of the MIMO signals may be pre-coded with a corresponding pre-coding scheme. In addition, the MIMO signals may be spatially multiplexed and transmitted in the same time-frequency slot.
An extension to MIMO makes use of multiple transmission points (each of which may be a set of geographically co-located transmit antennas) to transmit to a single UE or a group of UEs. The transmissions from the multiple transmission points may occur at different times and/or at different frequencies so that the UE (or the group of UEs) will receive transmissions from all of the multiple transmission points over a time window. This operating mode may often be referred to as multiple point transmission. As an example, at a first time, a first transmission point may be employed to transmit data to a UE, at a second time, a second transmission point may be employed to transmit data to the UE, and so on.
Coordinated multiple point (CoMP) transmission is one form of multiple point transmission, wherein the transmission made by the multiple transmission points are coordinated so that the UE or the group of UE may be able to either combine the transmissions made by the multiple transmission points or avoid interference to improve overall performance. A transmission point may be an eNB, a part of an eNB, a remote radio head coupled to an eNB and the like. When the UE transmits data to an eNB, a CoMP based reception means the transmitted data from the UE will be received by a plurality of geographically separated eNBs. On the other hand, when the UE receives data, the data to the UE may be instantaneously transmitted from a plurality of transmission points.
As an extension to multiple point transmission systems, coordinated multiple point (CoMP) transmission and reception is adopted for Long Term Evolution Advanced (LTE-A) to further improve channel utilization and overall performance. CoMP helps to enable the dynamic coordination of transmission and reception of a plurality of base stations. More particularly, when a mobile station is located at an overlapped region loosely covered by a plurality of base stations, CoMP helps to coordinate the base stations so that the base stations are able to jointly transmit user data to the mobile station. In addition, through a dynamic base station selection scheme, CoMP helps to find a base station and enable the base station to transmit user data to the mobile station. In order to better coordinate a plurality of base stations serving a mobile station, the channel property feedback information such as channel status information from mobile stations to a network entity is required.
CoMP transmission has been considered as a fundamental element for the next generation wireless communications systems. For example, in Third Generation Partnership Project (3GPP) Long Term Evolution Advanced standards compliant communications systems, CoMP transmission is an effective tool to improve the coverage of high data rates, cell-edge throughput, and/or to increase overall communications system throughput in both high load and low load scenarios. As such, by employing CoMP, a LTE-A system may achieve better coverage and capacity.